Sensor assembly for seat occupant weight classification system

ABSTRACT

A method and apparatus is provided that classifies a seat occupant into one of several different weight classes based on an estimated value of the seat occupant weight. An occupant&#39;s measured weight varies when the occupant&#39;s seating position changes or when the vehicle travels over adverse road conditions. A plurality of weight sensors are used to measure the weight exerted by a seat occupant against a seat bottom and are used to determine center of gravity for the seat occupant. A seat belt force sensor is also used to assist in classifying the seat occupant. Compensation factors using the seat belt force and center of gravity information are used to generate an estimated weight value. The estimated value of the occupant weight is compared to a series of upper and lower weight thresholds assigned to each of the weight classes to generate an occupant weight sample class. Over a period of time, several estimated weight values are compared to the weight class thresholds. Once a predetermined number of consistent and consecutive occupant weight sample classes is achieved, the occupant is locked into a specific occupant weight class. When the weight class is locked, the separation value between the upper and lower thresholds is increased to account for minor weight variations due to adverse road conditions and changes in occupant position.

RELATED APPLICATION

This application is a continuation of Ser. No. 10/603,992, filed Jun.25, 2003, which was a divisional of Ser. No. 09/965,390 filed on Sep.27, 2001, which claims the benefit of provisional application 60/236,456filed on Sep. 29, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for measuring theweight of a seat occupant and classifying the occupant into a weightclass.

2. Related Art

Most vehicles include airbags and seatbelt restraint systems that worktogether to protect the driver and passengers from experiencing seriousinjuries due to high-speed collisions. It is important to control thedeployment force of the airbags based on the size of the driver or thepassenger. When an adult is seated on the vehicle seat, the airbagshould be deployed in a normal manner. If there is an infant seat orsmall adult/child secured to the vehicle seat then the airbag should notbe deployed or should be deployed at a significantly lower deploymentforce. One way to control the airbag deployment is to monitor the weightof the seat occupant.

Current systems for measuring the weight of a seat occupant are complexand expensive. These systems use various types of sensors and mountingconfigurations to determine seat occupant weight. For example, somesystems use pressure sensitive foil mats or a plurality of individualsensors mounted within a seat bottom foam cushion while other systemsmount sensors on seat tracks, seat frame members, or other seatstructural members. The combined output from the sensors is used todetermine the weight of the seat occupant. The accuracy of the weightmeasurements from these types of sensor systems can be compromised dueto additional seat forces resulting from the occupant being secured tothe seat with a seatbelt.

For example, weight sensor systems can have difficulty identifying anadult, a child, or a car seat when the seatbelt is being used. When achild seat is secured to a seat with a seatbelt, an excess force acts onthe sensors mounted within the rear portion of the seat bottom, whichinterferes with accurate weight sensing. Over tightening of the seatbeltto securely hold the child seat in place, pulls the child seat downagainst the rear part of the seat bottom, causing the excessive forcemeasured by the sensors. Due to this effect, the current weight sensingsystems have difficulty in discerning between an adult belted to a seatand a child seat secured to the seat with a seatbelt.

In order to address this problem, sensors have been incorporated intothe seatbelt to measure the tension force applied to the seatbelt aspassengers or a child seat is secured to the seat. High seatbelt tensionforces indicate that a child seat is secured to the seat. Onedisadvantage with current seat belt force sensors is that it isdifficult to get accurate seat belt force measurements. Anotherdisadvantage with current seat belt force sensors is that non-axialloading on the belt can affect the accuracy of the force measurement.

Once seat occupant weight force measurements and belt force measurementsare taken, the seat occupant is typically classified into apredetermined classification. Some systems attempt to classify seatoccupants into predetermined customer-specified classes usually basedonly on occupant weight. The classification information is then used tomodify the deployment of the airbag. These systems do not provideaccurate and consistent classification over a wide range of adverse roadconditions and/or occupant seating conditions.

The accuracy of the weight measurements from known sensor systems canalso be compromised due to variable seat forces resulting from momentaryevents such as rough road conditions or seat occupants adjusting seatposition, for example. These types of events can transfer or removeweight from the seat for short periods of time, which affects theaccuracy of the system.

Thus, it is desirable to have an improved seat occupant weightmeasurement and classification system that provides increased accuracyin weight measurement and classification as well as overcoming any otherof the above referenced deficiencies with prior art systems.

SUMMARY OF THE INVENTION

A weight classification system utilizes weight and seat belt forcesensors to classify seat occupants into a predetermined weightclassification. Preferably, a plurality of weight force sensors aremounted between a seat bottom and a vehicle structure and a seat beltforce sensor is installed within a seat belt assembly. The weightsensors are preferably located at four connecting points for the seatframe and pick up all distributed forces (positive and/or negativeforces) to determine the total weight on the seat and the center ofgravity. The center of gravity and total weight determinations are usedto classify the seat occupant, which is further used to controldeployment of a safety device, such as an airbag.

In the preferred embodiment, one weight sensor is mounted at each cornerof the seat bottom. Each weight sensor includes a bending element havingone end mounted to the seat frame and an opposite end mounted to avehicle or other seat structure such as a riser, seat track, or vehiclefloor, for example. At least one strain gage assembly is mounted on acenter portion of the bending element and an integrated electronicspackage electrically connects the strain gage to an electronic controlunit (ECU) or other similar device. The strain gages measure deflectionof the center portion and generate a weight signal that is sent to theECU.

Preferably, the bending element includes a top surface and a bottomsurface with at least one centrally formed groove in one of the top orbottom surfaces. The groove extends at least partially along the widthof the sensor to localize strain in the center portion. The strain gageis placed on the other of the top or bottom surfaces, in an opposingdirection from the groove.

Output from the sensors near the front of the seat bottom are combinedand compared to output from the sensors near the rear of the seat bottomto determine the center of gravity. The initial seat occupant weight canbe adjusted to take into account the center of gravity of the seatoccupant. The initial seat occupant weight can also be adjusted to takeinto account forces exerted on the seat occupant by the seat beltassembly.

The seat belt sensor includes a load cell with a strain gage that isintegrated into a seat belt mechanism that is used to secure an occupantto a vehicle seat. When the seat belt is tightened, the sensor is pulledinto tension and this is measured by the strain gage. The strain gagemeasurements and signals are sent to the ECU. The ECU uses theinformation to determine whether a child seat or an adult is secured tothe vehicle seat. Further, the seat belt force information is used toadjust the initial seat occupant weight and is used to properly classifythe seat occupant.

The seat occupant is classified into one of several different weightclasses based on an estimated value of the seat occupant weight. Each ofthe weight classes has upper and lower thresholds that define the class.Over time, several comparisons are made between the estimated weight andthe thresholds of the weight classes and each comparison results in aweight class sample. The seat occupant is assigned a specific weightclass designation once a predetermined number of consistent andconsecutive weight class samples is achieved. The specific weight classdesignation remains locked until a certain number of inconsistent weightclass samples are observed.

In a disclosed embodiment of this invention, the method for classifyinga seat occupant into a weight class includes the following steps. Theseat occupant weight is measured resulting in an estimated weight. Theestimated weight is compared to a series of weight classes withthresholds to determine a class sample. The previous steps are repeateduntil a predetermined number of class samples having the same value isachieved and the class sample becomes locked as the occupant weightclass.

Additional steps include generating an occupant weight class signalcorresponding to the locked occupant weight class, transmitting theoccupant weight class signal to a control unit, and modifying deploymentof an airbag based on the occupant weight class signal. The weight classis unlocked when a predetermined number inconsistent class samples isobserved. When the class is unlocked, the process repeats.

Once the occupant has been classified into a weight class, that classbecomes the known class for the next comparison. Preferably, each weightclass is assigned an upper threshold and a lower threshold. At eachiteration, the estimated weight is compared to the upper and lowerthresholds for the last known weight class. The new class sample isdesignated the same as the last known weight class if the estimatedweight is between the upper and lower thresholds for the last knownweight class. The sample is set equal to a next higher weight class ifthe estimated weight is greater than the upper threshold for the lastknown weight class or the class sample is set equal to a next lowerweight class if the estimated weight is less than the lower thresholdfor the last known weight class.

In one disclosed embodiment, the value of the upper threshold of theclass sample is increased by a first predetermined amount and the valueof the lower threshold of the class sample is decreased by a secondpredetermined amount after the class sample is locked. The upper andlower thresholds are returned to their initial values when the classsample becomes unlocked.

The subject invention uses seat occupant weight and seat belt forcemeasurements in combination with varying weight class thresholds andclass sample histories to produce a more stable, accurate and robustclassification process that reduces errors caused by changes in occupantseating position and adverse road conditions. The more accurateclassification system is used to generate control signals, which areused to modify airbag deployment.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a vehicle with an airbag system andan occupant sitting in a seat with the airbag in an active state shownin dashed lines.

FIG. 2 is a front view of a seat and seat belt assembly showingdifferent installed positions of the seat belt force sensorincorporating the subject invention.

FIG. 3A is a top view of a seat belt force sensor.

FIG. 3B is a perspective view of FIG. 3A showing the seat belt forcesensor installed within a seat belt assembly.

FIG. 4 is a side view of the seat belt force sensor of FIG. 3A.

FIG. 5 is a schematic control diagram of the seat belt force sensor andcontrol system.

FIG. 6 is an exploded view of a seat assembly incorporation occupantweight sensors.

FIG. 7 is a side cross-sectional view of a weight sensor installed in aseat assembly.

FIG. 8 is a perspective view of the weight sensor of FIG. 7.

FIG. 9 is a schematic control diagram of the weight sensor and controlsystem.

FIG. 10A is a top perspective view of a weight sensor.

FIG. 10B is a bottom perspective view of the weight sensor of FIG. 10A.

FIG. 10C is a side view of the weight sensor of FIG. 10A.

FIG. 10D is a schematic diagram of an electronics package for a weightsensor.

FIG. 11 is a graph showing the relationship between track and lockthresholds.

FIG. 12 is a flowchart describing the method of determining a weightclass sample.

FIG. 13 is a flowchart describing the tracking and locking processes.

FIG. 14 is a schematic diagram of an ECU used in the control system.

FIG. 15A is perspective view of the ECU.

FIG. 15B is a perspective of the ECU of FIG. 15A from an opposing side.

FIG. 16 is a flowchart describing the overall control system operation.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

A vehicle includes a vehicle seat assembly, shown generally at 12 inFIG. 1, and an airbag system 14. The seat assembly 12 includes a seatback 16 and a seat bottom 18. A vehicle occupant 20 is secured to theseat 12 with a seat belt assembly 22. The vehicle occupant 20 can be anadult, child, or infant in a car seat secured to the seat 12 with theseat belt 22. A tension force Ft is exerted on the seat belt 22 thatrepresents the force is exerted against the occupant 20 as the belt istightened. The occupant 20 also exerts a vertical weight force Fwagainst the seat bottom 18. The subject weight classification systemmeasures the tension force Ft and the weight force Fw, determines theseat occupant weight and center of gravity, and classifies the seatoccupant. The classification information is used to control deploymentof a safety device, such as an airbag 24.

The airbag system 14 deploys the airbag 24 under certain collisionconditions. The deployment force for the airbag 24, shown as deployed indashed lines in FIG. 1, varies depending upon the type of occupant 20that is belted to the seat 12. When an adult 20 is belted to the vehicleseat 12, the airbag 24 should be deployed in a normal manner shown inFIG. 1. If there is small adult or an infant in a car seat secured tothe vehicle seat 12 then the airbag 24 should not be deployed or shouldbe deployed at a significantly lower force. Thus, it is important to beable to determine whether there is an adult 20 belted to the seat 12 orwhether a small adult or infant seat is secured to the seat with a seatbelt 22. One way to determine this is by monitoring the tension exertedon the seat belt 22. When an adult 20 is belted to the seat, normal seatbelt forces are exerted against the seat belt 22. When an infant orchild seat is belted to the seat 12, high tension forces are exerted onthe seat belt 22 because the seat belt 22 is overtightened to securelyhold the child seat in place.

The vehicle seat 12 is mounted to a vehicle structure 26, such as thefloor, in a manner well known in the art. The subject weightclassification system uses a plurality of sensors, some mounted in theseat bottom 18 to measure seat occupant weight and some mounted in theseat belt assembly 22 to measure the seat belt tension force Ft. Theoutput from the sensors that measure seat occupant weight is used todetermine an initial seat occupant weight and a seat occupant center ofgravity. The center of gravity information along with the output fromthe sensors that measure seat belt forces is used to generate acompensation factor that is used to adjust the seat occupant weight totake into account variations seat occupant position. The seat occupantis then classified into a predetermined weight classification by amethod that filters out momentary events such as rough road conditionsor seat occupants adjusting seat position. The preferred sensors formeasuring occupant weight and seat belt forces as well as the method forclassifying the seat occupants will be discussed in detail below.

The seat belt 22, shown more clearly in FIG. 2, has a strap portion 28that includes a shoulder harness and/or lap belt that is connected to amale buckle member 30. A seat belt latch mechanism 32 is hard mounted tothe seat 12 and typically extends outwardly from the seat 12 between theseat back 16 and the seat bottom 18. The latch mechanism 32 includes afemale receptacle 34 that receives the male buckle member 30 to securethe occupant 20 or child seat to the seat 12. The strap portion 28 canbe manually or automatically tightened once the belt is buckled to adesired tension.

A sensor assembly 40 for measuring the tension forces in the seat belt22 is shown in FIGS. 3A-3B and 4. The sensor assembly 40 includes arigid member that is preferably formed as a metallic plate 42 from4130Rc39 material, however, other similar materials could also be used.The plate 42 includes a first end 44 that is attached via a ioopconnection 46 to material 43 (see FIGS. 1 and 2) that forms a portion ofthe seat belt 22 (see FIG. 4) attached to the male buckle member 30 (asschematicafly indicated in dashed lines at 40 in FIG. 2) or femalereceptacle 34 (as schematically indicated in solid lines at 40 in FIG.2), and a second end 48 that is attached to a vehicle structure such asa B-pillar or seat latch mechanism 32.

The plate 42 includes a necked portion 50 positioned between the ends44, 48 that is narrower than the ends 44, 48. A strain gage 52 ismounted on the necked portion 50. The tightening of the seat belt 22exerts a tension force F_(T) on the plate 42 via the looped connection46, which results in strain on the necked portion 50. The strain gage 52measures this strain. The strain gage 52 is preferably a full bridgestrain gage with four (4) grids.

The first end 44 of the plate 42 is preferably positioned at an anglerelative to the necked portion 50 and the second end 48, shown in FIG.4. This causes the tension force to be applied at an angle, whichcreates a moment MT at one edge of the necked portion 50. The second end48 of the plate 42 is hard mounted to a vehicle structure 62 creating areaction force Frea and moment Mrea. The strain gage 52 measures thestrain resulting in the necked portion 50 of the plate 42 as the tensionforce FT is applied to the first end 44 of the plate 42.

An electrical connector 54 is also mounted on the plate 42 adjacent tothe strain gage 52. As shown in FIG. 5, the strain measurements aregenerated as signals 56 that are sent from the gage 52 to the connector54 and then to an individual electronic control unit (ECU) ormicroprocessor 58, see FIG. 5. The ECU 58 can be incorporated into theconnector 54 to include the necessary electronics and printed circuitboard (as shown in FIGS. 3A-3B ) or can be a separate component at aremote location on the vehicle, as discussed below. The ECU 58 processesthe strain signals 56 to determine the magnitude of the tension forcesFt exerted on the seat belt 22 and sends a seat belt force output signal66 to a central electronic control unit (ECU) or central microprocessor60, which uses the seat belt force signal and occupant weightmeasurements to classify the seat occupant and to ultimately controldeployment of the airbag 24. It should be understood that the ECU 58 canbe a separate unit or can be incorporated into the central ECU 60.

The strain gage 52 measures the strain caused by the tension force F_(T)in the seat belt 22 resulting in the generate of the seat belt forceoutput signal 66. The central ECU 60 uses the seat belt force outputsignal 66 to adjust or compensate the measured seat occupant weight forover-tightened seat belts. Further, the seat belt force output signal 66can be used to identify a child seat. If the tension force F_(T) exceedsa predetermined limit the system identifies a child seat. For example,an adult can experience a tension force in a seat belt up toapproximately 30 pounds (lbs) and still be comfortable. If the straingage 52 measures a tension force F_(T) that exceeds 30 lbs then thatwould indicate that a child seat has been belted to the seat 12. Once achild seat has been identified as the seat occupant, then the airbag 24would not be deployed during a collision. It should be understood that30 lbs is an approximate value, which can vary due to differing seat andseatbelt configurations. Thus, the predetermined limit for comparison tothe measured tension force F_(T) can also vary depending upon the seatconfiguration.

The sensor system for measuring seat occupant weight is shown in FIG. 6.A plurality of seat occupant weight sensors 68 are mounted to seatstructural member such as a seat frame or track member, generallyindicated at 70 in FIG. 6.

As discussed above, the seat 12 is preferably mounted to the vehiclestructure 26 on an inboard track assembly 70 a and an outboard trackassembly 70 b that is spaced apart from the inboard track assembly 70 aby a predetermined distance. Both the inboard 70 a and outboard 70 btrack assemblies include first 72 and second 74 track members.

The first track member 72 is typically mounted to a seat riser 76 ordirectly to the vehicle structure 26, such as the floor. The secondtrack member 74 is mounted for sliding movement relative to the firsttrack member 72 so that seat 12 position can be adjusted forwardly andrearwardly within the vehicle to a desired position.

The plurality of sensor assemblies 68 are mounted between the firsttrack members 72 of the inboard 70 a and outboard 70 b track assembliesand the riser 76. In the preferred embodiment, four (4) sensorassemblies 68 are used with a first sensor assembly 68 a positioned nearthe front of the inboard track assembly 70 a, a second sensor assembly68 b positioned near the rear of the inboard track assembly 70 a, athird sensor assembly 68 c positioned near the front of the outboardtrack assembly 70 b, and a fourth sensor assembly 68 d positioned nearthe rear of the outboard track assembly 70 b.

The sensor assemblies 68 are preferably installed as described above,i.e. between the lower seat track 72 and the riser 76. However, thesensor assemblies 68 can also be installed between the lower seat track72 and a reinforced floor plan or reinforcement bracket.

Preferably, each sensor assembly 68 a (left front portion of seat bottom18), 68 b (left rear portion of seat bottom 18), 68 c (right frontportion of seat bottom 18), and 68 d (right rear portion of seat bottom18) has a first end 78 mounted to the first track member 72 with atleast one fastener 80 and a second end 82 mounted to the riser 76 withat least one fastener 80, as shown in FIG. 7. It should be understoodthat any type of fastener can be used and that other joining methodsknown in the art can also be used to mount the sensors 68, however, M10fasteners are preferred. A central bendable portion 84 extends betweenthe first 78 and second 82 ends of the sensor assembly 68. As thevertical force Fw of the seat occupant 20 is exerted on the seat bottom18, the central bendable portion 84 of each sensor assembly 68 a, 68 b,68 c, 68 d deflects or bends into an S-shaped configuration putting oneportion of the sensor 68 in compression and another portion in tension.

As shown in FIGS. 7 and 8, the first 78 and second 82 ends are raisedabove/below the central bendable portion 84 to form steps 86 on eachside of the central bendable portion 84. The height of the steps 86 canbe varied. This configuration forms gaps between the sensor 68 and thetrack member 72 and between the sensor 68 and the riser 76 to facilitatebending.

A strain gage 88 is mounted to each of the sensors 68 a, 68 b, 68 c, 68d to measure the amount of bending in the central portion 84. Thesensors 68 have a top surface 90 facing the seat bottom 18 and a bottomsurface 92 facing the riser 76. Preferably, a combination of four (4)strain gages, forming a full bridge, are mounted on one of the top 90 orbottom 92 surfaces to measure the bending. The four strain gates arethus combined to serve as a Wheatstone Bridge for measuring deflection.The operation of a Wheatstone Bridge is well known in the art.

As shown in FIG. 8, the strain gage 88 is mounted on the top surface 90of the sensor 68. A first aperture 94 is formed at the first end 78 ofthe sensor 68 and a second aperture 96 is formed at the second end 82 ofthe sensor 68 for receiving the fasteners 80. The strain gage 88 ispositioned between the apertures 94, 96 on the top surface 90. In orderto achieve more accurate readings, full-bridge strain gage 88 shouldhave all strain gage components mounted on only one surface of thesensor 68. In other words, if the strain gage 88 is mounted on the topsurface 90 then no strain gage components should be mounted on thebottom surface 92 or if the gage 88 is mounted on the bottom surface 92,then no strain gage components should be mounted on the top surface 90.

Preferably, the sensors 68 are capable of a measuring range of −100kilograms to +100 kilograms with a resolution of 0.1 kilograms. Furtherthe sensors 68 are preferably designed to withstand 1500 pounds of forcewithout performance degradation.

The sensors 68 a, 68 b, 68 c, 68 d each generate a signal representativeof the occupant weight that causes bending at the respective location ofthe sensors 68 a, 68 b, 68 c, 68 d, see FIG. 9. Thus, the first sensor68 a generates a first signal 100, the second sensor 68 b generates asecond signal 102, the third sensor 68 c generates a third signal 104,and the fourth sensor 68 d generates a fourth signal 106. The signals100, 102, 104, 106 are transmitted to a common interface unit 108 andare then fed into the central processor unit or electronic control unit(ECU) 60 as is known in the art. The sensors 68 a, 68 b, 68 c, 68 doutput an amplified and digitized signal to the ECU 60 for final signalconditioning. The ECU 60 combines the signals 100, 102, 104, 106 todetermine the total weight of the occupant 20.

The sensors 68 can be susceptible to errors that can distort the weightmeasurement. Changes in temperature can result in base materialexpansion, resistance changes, and bonding changes. Further there can beinitial offset error and part-to-part variation between the bendableportion 84 and the strain gage 88 can affect gain. To reduce theseerrors, the strain gage 88 is preferably encapsulated, and the bendableportion 84 is designed to provide as much signal output as possible, thedesign of which will be discussed in further detail below.

Each sensor 68 includes an electronics package 140 that has a flexibleprinted circuit board (PCB) 142 and an application specific integratedcircuit (ASIC) 144, shown in FIG. 10D. This package 140 can be used withthe sensor 110 shown in FIGS. 10A-D or the sensor 68 shown in FIGS. 7and 8. To further reduce sensor error, decoupling and differentialcapacitance is provided at the PCB 142. The sensor signal conditioningASIC 144 is used to provide initial offset compensation and to measuretemperature for temperature compensation in the ECU 60. In additional tothese features, the ASIC 144 provides amplification, signal analog todigital conversion, compensation parameter storage, serial communicationof load signal, and diagnostics.

Each sensor 68 and electronics package 140 is preferably assembled inthe following manner. The surface of the sensor 68 is prepped. Cablesare bonded in a flexible-strip connector 146, which is attached to thestrain gage 88. The flexible-strip connector 146 and strain gage 88 arebonded to the bendable portion 84. The flexible-strip connector 146 issoldered to a housing 148 that surrounds the PCB 142 and ASIC 144. Thestrain gage 88 is preconditioned as is known in the art and the PCB 142is attached into the housing 148 with press-fit pins (not shown). Acover (not shown) is welded onto the housing 148 and the sensor 68 iscalibrated.

As discussed above, the ECU 60 combines the weight sensor signals 100,102, 104, 106 to determine the total weight of the occupant 20. The leftfront sensor 68 a and the right front sensor 68 c are combined todetermine a front weight portion and the left rear sensor 68 b and rightrear sensor 68 d are combined to determine a rear weight portion. Thefront and rear weight portions are compared to determine the center ofgravity. The total weight of the seat occupant 20 can then be adjustedby the ECU 60 to account for variations due to the center of gravityposition of the occupant. Further the ECU 60 can adjust or compensatefor seat belt forces acting on the seat occupant 20 as discussed above.

A preferred embodiment of a weight sensor 110 is shown in FIGS. 10A-10C.In this preferred embodiment, each of the sensor assemblies 110 a, 110b, 110 c, 110 d includes at least one groove 112 formed in one of thetop 90 or bottom 94 surfaces of the sensor 110. The groove 112 extendsat least partially along the width of the sensor assembly 68 to localizestrain in the central bendable portion 84. The full bridge strain gage88 is placed on the opposing surface, facing an opposite direction fromthe groove 112, see FIG. 10B. As shown, the groove 112 preferablyextends across the entire width of the sensor 68.

By measuring the deflection in all four (4) locations in the inboard 70a and outboard 70 b track assemblies, it is possible to calculate theoccupant weight, which is proportional to the sum of the output of allof the sensors 68 a, 68 b, 68 c, 68 d. The electronics for signalconditioning and the interface 108 can be housed within the trackassemblies 70 a, 70 b as is well known in the art.

Once the weight and seatbelt forces have been measured, the occupant 20is placed into a weight classification. The weight signals 100, 102,104, 106 are combined and initially represent an estimated weight signal114 for the occupant 20. The ECU 60 compares the weight signal 114 to aseries of weight classes each having at least one threshold value,assigns a weight class designation to the occupant 20, and generates anoutput control signal 116 that controls and modifies deployment of theairbag 24 based on the weight classification. The classification processwill be discussed in greater detail below.

The weight sensors 68 are preferably calibrated prior to installation.Mounting the seat 12 in the vehicle induces stresses in the seat trackassemblies 26 that are then seen in the sensors 68. These stresses canvary from seat to seat and represent an offset value. During systemdiagnostics, the sensors 68 can be re-calibrated. To re-calibrate, theseat 12 must be empty. Once sensor output is stabilized, the zero valuesare then restored. This procedure can also be used to compensate forsensor wear that occurs over time.

As discussed above, the ECU 60 (shown schematically in FIG. 14) receivessignals from the weight sensors 68 and the seat belt force sensor 40 anduses this information to classify seat occupants 20. The ECU 60 includesthree (3) main sections: power regulation 60 a, microprocessing 60 b,and communication 60 c. The signals 66, 100, 102, 104, 106 are receivedand processed by the ECU 60 to make an approximation of the weightclassification. After the ECU 60 makes a determination, a message isplaced on a communications bus for the vehicle to use properly.Diagnostics are periodically performed to check the functionality ofsuch components as the microprocessor, the sensors 40, 68, communicationbus, input voltage, etc., for example.

After power down, the ECU 60 preferably stays alive to perform systemcalibration to adjust for offset that may occur over time. The ECU 60can put itself and the sensors 40, 68 to sleep after calibrations arecompleted to conserve vehicle energy.

As shown in FIGS. 15A and 15B, the ECU 60 preferably includes a plastichousing 120 with integrated insert molded sealed connectors 122 forattachment/connection to the sensors 40, 68. These types of connectors122 simplify installation and interface connections.

The weight measurements taken by the sensors 68 can vary as the occupant20 changes seating positions and can vary as the vehicle travels throughvarious maneuvers and over different types of roads. In order to providea consistent and accurate weight classification, the classificationprocess must filter out these variations. The subject invention monitorsthe occupant's estimated weight and compares the estimated weight to aseries of weight class thresholds to determine an individualclassification sample. A history of these class samples is observed andrecorded by the ECU 60. Once a predetermined number of consistent andconsecutive samples are observed, the class sample is locked as theoccupant's weight class. Over time, a plurality of comparisons are madebetween the estimated weight and the weight class thresholds.

Each weight class is assigned a predetermined upper threshold and apredetermined lower threshold. The number and values for the upper andlower thresholds can be varied. Each weight class sample is determinedby comparing the occupant's estimated weight against the previous weightclass sample's thresholds. If the estimated weight falls between theupper and lower thresholds for that previous class, the current classsample is set to that last sample. If the estimated weight does not fallbetween the upper and lower thresholds for that previous class, eitherthe weight class above or the weight class below the previous weightclass is set for the current weight class depending on which thresholdis crossed. Preferably, only one incremental weight class change ispermitted for each iteration. Allowing a change of only one class periteration helps to smooth the transition between the classes.

The upper and lower thresholds for each class varies depending onwhether the process is in the track mode or the lock mode. If the systemis locked onto a specific weight class, the separation between the upperand lower thresholds for that weight class is increased to provide morehysteresis. By increasing the hysteresis when locked, it is moredifficult to change or unlock the weight class designation. This helpsto filter out unintended weight class changes, i.e., error induced byadverse road conditions or changes in occupant seating position. FIG. 11shows the relationship between the track and lock thresholds. Note thatthe track upper and lower thresholds for weight class two (2) are closertogether than the lock upper and lower thresholds for weight class two(2). Thus, the upper threshold for weight class (2) is increased and thelower threshold is decreased when class (2) is the locked class.

FIG. 12 is a flow chart showing the process for determining the currentweight class sample. When the process is started, there is adetermination of whether the process is in the track or lock mode. Ifthe process is in the track mode than the current estimated weight iscompared to the previous class' track lower threshold. If the currentestimated weight is less than the previous class' track lower thresholdthan the next lower weight class is set as the current weight class. Ifthe current estimated weight is not less than the previous class' tracklower threshold than the estimated weight is compared to the previousclass' track upper threshold. If the current estimated weight is greaterthan the previous class' track upper threshold than the next higherweight class is set as the current weight class. If the currentestimated weight is not greater than the previous class' track upperthreshold than the current weight class is the same as the previousweight class. A similar method is used when the process is in the lockmode except the current estimated weight is compared to the previousclass' lock upper and lower thresholds.

As the process moves through each iteration, a history of thecomparisons between the estimated weight and the weight class thresholdsis observed and recorded, see FIG. 13. The weight class samples aremonitored, looking for the same class sample to be repeated. The processstarts counting or tracks consecutive samples of the same weight class.If a non-consistent sample is observed, the count is reset to zero. Whena predetermined number of consistent and consecutive samples isobserved, that observed weight class becomes locked. Once a class islocked, it remains the designated occupant weight class until a specificnumber of consecutive weight class samples above or below the lockedclass is observed. If the lock is lost, the process starts tracking thenumber of consecutive weight classes again and the process is repeated.The output is either the tracked or locked weight class, depending onthe mode. If a class is locked, the locked class is the output class. Ifa class is not locked, the track weight class is the output class. Thetrack/lock feature helps to filter out class changes caused by occupants20 that change position, class changes caused by adverse roadconditions, and class changes resulting from sudden vehicle maneuverssuch as turning or braking.

Preferably, the class update rate is approximately one update everysecond and the weight class locking delay is at least five (5) seconds.Preferably the locking delay is approximately between five (5) and seven(7) seconds. This delay period filters out momentary events that maytransfer or remove weight from the seat, e.g., due to rough roadconditions or seat occupant body movements. These momentary events aretypically important for borderline cases. If the same weight class iscalculated for five to seven seconds the class is locked. This widensthe window for the determination of the current weight class. A weightoutside of the window must be maintained for five to seven seconds tounlock and change the weight class. These times can be adjusted throughcalibration. An unlocked system can change weight classes every second.While these are the preferred time periods, it should be understood thatthese time periods could vary depending on the application.

A flowchart summarizing the weight classification system is shown inFIG. 16. The weight sensors 68 a-d generate weight signals 102-106 thatare proportionate to the weight exerted against the seat bottom 18 atthe respective sensor location. The front sensors 68 a, 68 c arecombined to determine a front weight portion signal 130 and the rearsensors 68 b, 68 d are combined to determine a rear weight portionsignal 132. The front 130 and rear 132 weight portion signals arecompared to determine a center of gravity. An estimated seat occupantweight is then determined by using various compensation factorsincluding information from the seat belt force sensor 40, center ofgravity, and combined weight information from all weight sensors 68 a-d.This adjusted weight designation is then used to classify the seatoccupant by a process discussed above.

The number of classes and thresholds can be correlated to predeterminedrequirements that vary according to different specifications and vehicletypes. One example of a set of weight classes is as follows. If theweight determination is less than 8 kilograms the seat is determined tobe empty, if the weight determination is between 8 and 30 kilograms thesystem indicates a child is the seat occupant, if the weightdetermination is between 30 and 60 kilograms the system indicates asmall adult is the seat occupant, and if the weight determination isgreater than 60 kilograms the system indicates a large adult is the seatoccupant.

Although a preferred embodiment of this invention has been disclosed, itshould be understood that a worker of ordinary skill in the art wouldrecognize many modifications come within the scope of this invention.For that reason, the following claims should be studied to determine thetrue scope and content of this invention.

1. A vehicle weight classification system comprising: a seat assemblyhaving a seat frame for supporting a seat bottom; a seat belt assemblyfor securing a seat occupant to said seat assembly; a rigid memberattached to said seat belt assembly, said rigid member comprising asingle-piece component having a first end for supporting a seat beltportion and a second end integrally formed with said first end forattachment to a vehicle structure; a plurality of weight sensors mountedto said seat frame for generating a plurality of weight signals inresponse to a weight force applied to said seat bottom; at least oneseat belt force sensor for generating a seat belt force signal, saidseat belt force sensor being mounted directly to said rigid memberbetween said first and second ends for measuring a force exerted on saidrigid member by a tension force applied to said seat belt portion; anelectronic control unit for receiving said weight signals and seat beltforce signals to determine occupant weight and center of gravity,generating an occupant classification based on said occupant weight andcenter of gravity, and transmitting an output control signal based onsaid occupant classification; and an airbag module for receiving saidoutput control signal to control airbag deployment based on saidoccupant classification.
 2. A system according to claim 1 wherein saidseat assembly includes a seat mount for attachment to a vehicle floorand said plurality of weight sensors comprises a first sensor mounted ata front right side corner of said seat bottom between said seat frameand said seat mount, a second sensor mounted at a front left side cornerof said seat bottom between said seat frame and said seat mount, a thirdsensor mounted at a rear right side corner of said seat bottom betweensaid seat frame and said seat mount, and a fourth sensor mounted at arear left side corner of said seat bottom between said seat frame andsaid seat mount.
 3. A vehicle weight classification system comprising: aseat assembly having a seat frame for supporting a seat bottom; a seatbelt assembly for securing a seat occupant to said seat assembly; arigid member comprising a single-piece component having a body portion,a first end for supporting a seat belt portion of said seat beltassembly and a second end adapted for attachment to a fixed structurewherein said first and second ends are integrally formed with said bodyportion; a plurality of weight sensors mounted to said seat frame forgenerating a plurality of weight signals in response to a weight forceapplied to said seat bottom; at least one seat belt force sensor forgenerating a seat belt force signal, said seat belt force sensor beingmounted on said body portion of said rigid member between said first andsecond ends for measuring a force exerted on said rigid member by atension force applied to said seat belt portion; and an electroniccontrol unit for receiving said weight signals and seat belt forcesignals to determine occupant weight and center of gravity, generatingan occupant classification based on said occupant weight and center ofgravity, and transmitting an output control signal based on saidoccupant classification to control airbag deployment based on saidoccupant classification.
 4. A system according to claim 1 wherein saidfirst end includes a first opening to receive a portion of seat beltmaterial in a looped connection, and wherein said second end includes asecond opening to receive a fastener to secure said rigid member to thevehicle structure.
 5. A system according to claim 4 wherein said firstand second ends are non-coplanar.
 6. A system according to claim 1wherein said first end of said rigid member extends at an oblique anglerelative to said second end of said rigid member.
 7. A system accordingto claim 1 wherein said rigid member comprises a single plate with saidat least one seat belt force sensor being directly mounted to saidsingle plate.
 8. A system according to claim 7 wherein said single plateincludes a narrowing neck portion to which said at least one seat beltforce sensor is mounted.
 9. A system according to claim 3 wherein saidsingle-piece component comprises a single plate with said at least oneseat belt force sensor being directly mounted to said single plate. 10.A system according to claim 9 wherein said single plate includes anarrowing neck portion that supports said at least one seat belt forcesensor.
 11. A system according to claim 9 wherein said first end of saidsingle plate extends at an oblique angle relative to said second end ofsaid single plate.
 12. A system according to claim 1 wherein said secondend is to be directly attached to the vehicle structure.
 13. A systemaccording to claim 1 wherein said rigid member has a first surface toface the vehicle structure and a second surface facing opposite saidfirst surface, and wherein said at least one seat belt force sensor ismounted to said second surface.
 14. A system according to claim 13wherein said rigid member includes a first opening to receive said seatbelt assembly and a second opening to receive a fastener for attachmentto the vehicle structure, and wherein said at least one seat belt forcesensor is centrally positioned on said second surface and spaced apartfrom said first and said second openings.
 15. A system according toclaim 3 wherein said second end is to be directly attached to the fixedstructure.
 16. A system according to claim 3 wherein said body portionhas a first surface to face the fixed structure and a second surfacefacing opposite said first surface, and wherein said at least one seatbelt force sensor is mounted to said second surface.
 17. A systemaccording to claim 16 wherein said body portion includes a first openingat said first end to receive the seat belt portion and a second openingat said second end to receive a fastener for attachment to the fixedstructure, and wherein said at least one seat belt force sensor iscentrally positioned on said second surface and spaced apart from saidfirst and said second openings.